1. Field of the Invention
The present invention relates to an electronic equipment having a boost DC-DC converter.
2. Description of the Related Art
In recent years, it has been brought to attention to utilize electric power generated by a power generation device such as a fuel cell, a solar cell, or a thermal power generation device using a Seebeck effect from an environmental point of view. In the fuel cell, however, the generated electric power cannot follow a rapid load change, and an amount of the generated electric power for the solar cell or the thermal power generation device is fluctuated due to a surrounding environment. Thus, in a case where electric power of those power generation devices is directly supplied to a load circuit, it is difficult to stably operate the load circuit at a desired time. Accordingly, generally adopted is a method in which electric power outputted from those power generation devices is temporarily stored in an electric power storage device to drive the load by using the stored electric power.
Further, those power generation devices have been utilized as a power supply for a portable electrical equipment, so it is required to reduce the power generation devices in size. In order to reduce the power generation devices in size, it is necessary to reduce the number of cells of the fuel cell or the solar cell, and it is also necessary to reduce the number of series of P-type and N-type pillars. As a result, voltage of the electric power generated by those power generation devices is more likely to be lower than charging voltage of the electric power storage device, and the electric power generated by those power generation devices is difficult to directly charge into the electric power storage device in many cases.
For this reason, generally adopted is a method in which a boost DC-DC converter is provided between one of those power generation devices and the electric power storage device, electric power having low voltage generated by those power generation devices is converted into, in the boost DC-DC converter, boosted electric power which is boosted up to voltage which the electric power storage device can store, and the boosted electric power is charged into the electric power storage device.
FIG. 6 shows a configuration of a conventional electronic equipment in which electric power generated by a power generation device is charged into an electric power storage device by utilizing a boost DC-DC converter. The electronic equipment shown in FIG. 6 includes a power generation device 101 for generating electric power such as a fuel cell, a solar cell, or a thermal power generation device, a boost DC-DC converter 102 for boosting voltage of the electric power of the power generation device 101, an electric power storage device 103 for charging the boosted electric power outputted by the boost DC-DC converter 102, and a Schottky diode 401 for preventing stored electric power of the electric power storage device 103 from flowing reversely to the boost DC-DC converter 102. A generated electric power output terminal 107 of the power generation device 101 is connected to an input terminal 108 of the boost DC-DC converter 102. An output terminal 111 of the boost DC-DC converter 102 is connected to a power supply terminal 109 of the boost DC-DC converter 102 and a P-type electrode of the Schottky diode 401. An N-type electrode of the Schottky diode 401 is connected to a charging terminal 112 of the electric power storage device 103 (e.g., refer to JP 2004-120950 A).
With such the configuration, in the conventional electronic equipment, even when the voltage of the electric power generated by the power generation device is lower than the charging voltage of the electric power storage device due to downsizing of the power generation device, it is possible to charge this electric power into the electric power storage device. In addition, since the output terminal and the power supply terminal of the boost DC-DC converter are connected thereto, the boost DC-DC converter can operate by using a part of the boosted electric power which the boost DC-DC converter itself has converted and generated. As a result, the boost DC-DC converter can be driven with voltage higher than that used for operating the boost DC-DC converter using the electric power generated by the power generation device, thereby making it possible to enhance an electric power converting ability of the boost DC-DC converter. Further, if the boost DC-DC converter is activated, even in a case where the voltage of the electric power generated by the power generation device thereafter becomes lower than the voltage with which the boost DC-DC converter can operate, the boost DC-DC converter can charge the generated electric power into the electric power storage device while maintaining the operation thereof as long as the boosted electric power is sufficiently larger than the electric power used for operating the boost DC-DC converter.
Further, by providing the Schottky diode to the electronic equipment, it is possible to prevent the stored electric power of the electric power storage device from flowing reversely to the boost DC-DC converter in a case where power generation of the power generation device has been stopped.
In other words, in the conventional electronic equipment with the above-mentioned configuration, even when the voltage of the electric power generated by the power generation device is lower than the charging voltage of the electric power storage device due to downsizing of the power generation device, it is possible to charge the electric power into the electric power storage device. In addition, as long as the boost DC-DC converter is once activated, even when the voltage of the electric power generated by the power generation device is lower than the operating voltage of the boost DC-DC converter, it is possible to charge the electric power into the electric power storage device when the electric power is sufficiently supplied. Further, the conventional electronic equipment may have a feature that the stored electric power of the electric power storage device is consumed only by the load.
However, in the conventional electronic equipment with the above-mentioned configuration, a forward drop voltage is generated in the Schottky diode, which causes a charging loss when the boosted electric power of the boost DC-DC converter is charged into the electric power storage device. The charging loss increases as the charging voltage of the electric power storage device becomes lower. For example, when the charging voltage of the electric power storage device is 3.0 V, a forward drop voltage of the Schottky diode is normally about 0.2 V, so about 7% of the charging loss is caused.
Further, for the conventional electronic equipment with the above-mentioned configuration, also proposed is a method in which a switching device is provided in place of the above-mentioned Schottky diode, or a switching device is provided in an electric power supplying path from the output terminal of the boost DC-DC converter to the power supply terminal of the boost DC-DC converter, and in which the switching device is turned off when the electric power storage device is not charged, thereby preventing the stored electric power of the electric power storage device from being consumed by a drive of the boost DC-DC converter. In the method, however, a configuration of a circuit for detecting a case where the electric power storage device is not charged may become complicated, power consumption in the circuit may be increased, or the switching device may not be reliably controlled, thereby lowering charging efficiency in some cases.
In other words, in the conventional electronic equipment with the above-mentioned configuration, there arise problems in that the charging efficiency is lowered when the electric power generated by the power generation device is charged into the electric power storage device, or a manufacturing cost is increased because a complicated circuit is additionally provided for improving the charging efficiency.